1. Field of the Invention
The present invention relates to a method for stabilizing track jump in a disk drive, and more particularly, to a track jump stabilizing method of a disk drive wherein jump margin is stabilized by controlling the jump timing of the sled and the actuator.
The present application is based on Korean Application No. 59420/1995 which is incorporated herein by reference for all purposes.
2. Description of the Related Art
In general, referring to FIGS. 1 and 2, pickup 101 traces tracks of a disk by a tracking servo, and pickup body 117 jumps in accordance with the track playing since the tracking movement range of the object lens 201 driven by an actuator is limited. Also, in order to access a desired song, the pickup body 117 jumps to reach that song. At this time, the maximum jump range is conventionally set to within about .+-.200 tracks. When a targeted jump is beyond 200 tracks, access time is delayed due to focus drop or track oscillation. However, an excessive delay may cause degradation of the data. In a conventional manufacturing process, a jump algorithm has been adopted for mass tests of the deviation of the deck (change of a sign) or that of the drive circuit voltage.
In mass production of disk drives, the test algorithm of FIG. 4 is conventionally used. FIG. 3 is a control system diagram for explaining the conventional jumping algorithm. The control system is comprised of a command logic circuit 302, which receives from microcomputer 300 commands for controlling the tracking and the sled, and generating a sled driving control signal and a switching control signal. Pulse generator 303 is controlled by the output of the command logic circuit 302 to generate tracking kick/brake and sled driving control signals for pickup 306. Servo controller 304 controls the driving of the pickup and the sled. Switching unit 331 selects the tracking kick/brake and sled movement signals generated from the command logic circuit 302 or the sled and a pickup reproducing control signal of the servo controller to provide to the pickup 306.
Referring to FIG. 4, the microcomputer 300 generates a track jump command signal in step 4a. Then, the signal is analyzed at the command logic circuit 302 and applied to the pulse generator 303. The switching signal generated from the command logic circuit 302 and applied via switching control 313 turns on sled and tracking driving on/off switches 317 and 318 and makes switches 319 and 320 contact point 1. Thus, in step 4b, tracking is kicked as in FIG. 5A and the sled is kicked as in FIG. 5B, both being controlled to be concurrently driven (see 501 and 505 of FIGS. 5A and 5B). Correspondingly, the pickup 306 is driven and the control result of the pickup is applied to the servo controller 304. The servo controller 304 detects the zero crossing state (i.e., the state where a track is sensed) according to the driving state of the pickup 306 and informs the microcomputer 300. The microcomputer 300 counts the zero crossing states and checks whether the track zero crossing reaches 50 in step 4c. When the track zero crossing reaches 50, the microcomputer 300 brakes the tracking (see 504 of FIG. 5A) and applies a control signal for sled-off to the command logic circuit 302 (see 506 of FIG. 5B). The command logic circuit 302 outputs signals for tracking brake and sled-off to the pulse generator 303 and the pulse generator 303 generates corresponding signals to provide to the pickup 306 via the switches 317, 318, 319 and 320. At this time, the tracking assumes a braking state and the sled is turned off.
In step 4e, the microcomputer 300 checks whether the number of the zero crossing reaches 50 through the servo controller 304. When 50 is reached, in step 4f, tracking gain is turned on and the sled is turned on as in 502 of FIG. 5A. After time is delayed for 10 ms in step 4g, the switches 319 and 320 are positioned at a point 2 according to the signals of the command logic circuit 302 via switching control 313 so that the tracking is turned on in step 4h.
Considering the problem of jumping over 100 tracks, when continuous jumping over 100 tracks is made, tracking, i.e., actuator, reaches exactly 160 .mu.m.+-.10% (1.6 .mu.m.times.100 tracks) by checking the track zero crossing. However, the sled has an error of 25-30% (movement distance error of 160 .mu.m.+-.30%) due to the load deviation of the deck and that of sled voltage. The error becomes further considerable due to the deviation of the tracking and sled movement time as shown in FIG. 6.
FIG. 6 shows an example of when the actuator, the pickup 101 and the object lens 201, are concurrently moved 5 times at an error of 20%. When one jump covers 100 tracks, the margin becomes 75 tracks, assuming that the tracking of the object lens 201 and the sled driving of the pickup 101 occur concurrently as in the example of FIGS. 5A and 5B. Thus, the object lens 201 bumps the pickup 101 since 25 tracks are missed for every jump. Consequently, the focus drops and tracking oscillation occurs accordingly.
That is, since the pickup servo and the lens actuator have different operational characteristics (e.g., different response curve), if the track jump command is applied to both concurrently, the lens actuator may attempt to reach a track beyond the range allowed by the pickup servo. Specifically, if is the pickup servo is slow to respond to the jump command, it may take a short time before it can place the lens at a location where the target track is within the range of movement of the actuator. Therefore, if the actuator is attempting to reach that track prematurely, the lens will collide with the pickup wall.